Aleppo's citadel dominates Syria's second city, which vies with Damascus for the title of longest inhabited city and is famous as a centre of trade. It is thought that building on the mounddates back to around 350 BC but what stands today is mainly from the Mamluk era (1250 to 1517) and from the 12th century when the citadel was used by the Muslims during the Crusades.